[ATHENS] Early elections in Greece are "imperative" to maintain the country's political stability as it begins to implement an unpopular third debt bailout, a minister said Monday.

"Elections are imperative for purposes of political stability. Given the problems in the government's (parliamentary) majority, the situation can be called anything but stable," Energy Minister Panos Skourletis told Skai TV.

A third of MPs from the ruling radical left party Syriza last week rebelled against Prime Minister Alexis Tsipras in a vote on the three-year, 86-billion-euro (S$134 billion) package, forcing him to rely on opposition parties to ratify it.

"Such a major numeric loss of parliamentary majority is unprecedented," said Skourletis, a former spokesman for Tsipras.

But he added that he saw elections as "highly likely" in the coming months.

According to reports, Mr Tsipras will decide whether to call a confidence vote after a scheduled European Central Bank bond repayment on August 20.

However, the main opposition parties that have so far helped Mr Tsipras pass the reforms demanded by Greece's creditors through parliament have indicated that they will not back him in a confidence vote.

Syriza swept to power in January on a wave of public anger against steep tax rises, spending cuts and reforms demanded by Athens' creditors - the EU, European Central Bank and International Monetary Fund - in exchange for two previous bailouts.

After six months of fraught negotiations, and with capital controls since June to avert a bank collapse, Mr Tsipras on July 13 had to sign up to fresh cuts to keep the country in the eurozone.

Mr Skourletis on Monday reasoned that the government was bound by "democratic legality" to seek fresh popular approval as the "reality" it faced "bears very little relation to the mandate we received in the last elections."

There is a hefty list of measures on tax, competition, social security and pensions that must be voted through and brought into force by the end of the year, a task Mr Tsipras is unlikely to manage with so many of his lawmakers now arrayed against him.

A source close to Mr Tsipras said the embattled premier would start a range of meetings from August 20 with government officials to discuss strategy.

Meanwhile, 17 Syriza lawmakers launched an appeal on Monday for party unity and for the immediate holding of a party congress before any elections are held. None of the rebel MPs were among the lawmakers making the call.